The overall goals are to elucidate the molecular mechanisms by which cholera toxin activates adenylate cyclase in intact eukaryotic cells and to generate V. cholerae mutants that reduce defective toxins. More specifically, we are interested in the mechanism by which subunit A of cholera toxin activates adenylate cyclase, the mechanism for penetration of subunit A (or intact toxin) to the inner surface of the plasma membrane or to the cytosol and the precise structural features of the subunits of cholera toxin that are critical for adenylate cyclase activation and cell penetration. We will use toxin mutants to elucidate these mechanisms and we will determine if appropriate V. cholerae mutants will protect against the natural disease as this is manifested in experimental animals. BIBLIOGRAPHIC REFERENCES: Brasitus, T.A., Field, M., and Kimberg, D.V.: intestinal mucosal cyclic GMP: regulation and relation to ion transport. Am. J. Physiol. 231:275-282, 1976. Field, M.: Regulation of active ion transport in the small intestine. In: Acute Diarrhoea in Childhood, Ciba Foundation Symposium 42 (new series). Elsevier Excerptica medica/North-Holland, 1976.